Circling Cyclones

Since we’re currently in hurricane season, it seems a good time to talk about hurricanes and cyclones. These types of weather systems don’t often find themselves in a traffic jam in Earth’s vast oceans, but when they do, there are consequences.

When two storms move too close together, they start to influence one another’s strength and track. This tropical tango is known as the Fujiwhara effect. That scenario played out this week when Hurricanes Imelda and Humberto danced together off the southeastern US coast.

After devastating the coast of North Carolina, Humberto moved out to sea, but as it did so, it tugged Imelda to go with it.

On Tuesday (9/30), they were both Category 1 hurricanes and they were within 467 miles of each other, which is the closest that two Atlantic hurricanes have come to each other in at least the past 60 years. Two hurricanes churning side-by-side is more common in the Pacific Ocean but rarely happens in the Atlantic.

The interactions during these events can vary greatly, which can make forecasting the tracks and intensity a challenge. Imelda’s track forecast changed dramatically after she was pulled away from the US and toward Bermuda.

Both hurricanes struggled in the face of the other’s wind shear, with Humberto weakening and finally dissipating Wednesday morning. After that, forecasters expect Imelda to hit Bermuda on Thursday as a Category 2.

In 1921, Japanese meteorologist Sakuhei Fujiwhara published a paper that said two storms spinning near each other could start rotating together around a common center point. He was right.

How close the storms need to be to trigger the Fujiwhara effect is dependent on the size of each storm. If two large storms—those that span hundreds of miles—get within about 850 miles of each other, they start to dance. The distance shrinks to 350 miles for smaller storms.

Closely matched storms will orbit around a common point but then go their separate ways. The circling tugs each storm off the path they would have taken. In 2017, Hilary and Irwin had this experience in the east Pacific. They were well matched. Both systems interacted for so long, they eventually dissipated around the same time.

But if one storm is much stronger than the other, the stronger one could consume the weaker one. In the west Pacific in 2022, the powerful typhoon Hinnamnor was headed for Taiwan before it met a tropical depression that was trying to grow. Hinnamnor and the depression rotated until the typhoon devoured the depression. Hinnamnor slowed and weakened for a bit, but when it restrengthened, it took a nearly 90-degree turn from its original track.

In a rare Fujiwhara scenario, two weak storms spinning together could merge and create a larger storm,

All of these potential interactions and outcomes pose an incredible forecasting challenge, even for computers. Any small changes in the strength or size of each storm, or slight deviation from the anticipated track throws a model’s complex calculations into chaos.

 

https://www.nola.com/news/hurricane/hurricanes-humberto-imelda-fujiwhara/article_14cec9cf-1c86-422c-983d-71b320682d2b.html

https://www.msn.com/en-us/weather/topstories/here-s-what-can-happen-when-two-hurricanes-get-too-close-together/ar-AA1NiXg4?ocid=hpmsn&cvid=68d5abc4f3d04d0b915ca4e4134e1350&ei=63

What is This World Coming to 2?

Okay, we were talking about the sea and what climate change is doing to it. My examples last time were in Europe and the US, in the northern temperate zones. Now I want to consider all that ice and water in the extreme north and south, around the poles.

If you’ve been paying attention, you might remember news of huge chunks of Antarctic ice breaking away. I’m talking chunks bigger than some states. Antarctica is receiving warmer weather than it’s seen in millennia, or maybe even millions of years. Some coasts that certain types of penguin have called ‘home’ for countless generations are becoming inhospitable for them. They already live at the bottom of the world, where are they supposed to go from there?

The Arctic Ocean is not doing any better. There is no land under all that ice at the north pole, just water. You might think, ‘That’s okay, because it takes a lot of energy to warm water up.’ Yes, it does. And yet, that water under that thick sheet of ice has warmed up.*

If you look at a map or globe, you’ll see a bunch of islands above Canada. During Europe’s Age of Exploration, several well-provisioned ships made attempts to find a ‘Northwest Passage’ during the summers, trying to find a way to get around the Americas to do trade with the Orient. I don’t remember hearing of any of those excursions ever making it through, nor of any making it home again. At that time, I understand, whatever open channels of water that could be found among all those islands were unreliable and tended to close up and freeze a ship in place, even in summer. The last few years, so much of that ice has melted during the summer, that some cruise lines have offered cruises from one coast to the other, via the Canadian passage.

Something has happened to the Beaufort Gyre. That is a 60-mile-diameter pool of cold freshwater and sea ice located north of Alaska. It used to spin clockwise for 5-7 years, then slow down and start spinning in the opposite direction. This change in direction was caused by periodic cyclones that moved from the Northern Atlantic Ocean into the Arctic Ocean. But the North Atlantic has been warming up even faster than other parts of the world, and has failed to get the Beaufort Gyre to change direction in a dozen years or more.

So it’s just been sitting there, spinning and getting larger. And although it contains ‘cold’ water, that’s a matter of relativity. This spinning water contains twice as much heat now as it did 30 years ago. But it’s not sitting on top, like you’d think it would. It extends so deep, it is creeping under the Arctic ice sheet, which I understand can be a mile or more thick. Once it starts melting that ice sheet from below, well, how long before that ice sheet starts to break apart into gigantic icebergs, like the Antarctic ice has already started doing?

And what happens when all that ice breaks up and melts? Right, it raises sea level, which we discussed last time.

I had never heard of the Beaufort Gyre until a couple days ago, but I’m not done with it. From what I’ve been reading, whether it continues its current spin or starts going the other way, somebody’s in for a nasty time. Maybe it will come up next time.

* https://www.dailykos.com/stories/2018/9/5/1792312/-Warm-ocean-water-has-penetrated-deep-into-the-Arctic-interior-portending-year-round-loss-of-sea-ice